There’s not much to go on here, but also no real surprise. Amazon claimed 50% of online book sales in France in 2018, according to a report by Kantor World Panel.
According to the report Amazon was by far the largest online retailer in the country, and its biggest showing was in the books sector, with 50% of the online market, and not far behind with games and toys (44%).
No indication here of how ebooks and audiobooks fared, and more importantly no comparison with book sales from bricks & mortar store, so all this report tells us is that Amazon is the largest online book retailer, but not what share of the French book market Amazon has.